1. Field of the Invention
The present invention relates to a water in oil type (to be referred to as "W/O type", hereinafter) emulsion explosive.
2. Related Art Statement
A W/O type emulsion explosive was published for the first time by U.S. Pat. No. 3,161,551. Afterwards, various W/O type emulsion explosives have been proposed depending on the use purposes.
Heretofore proposed W/O type emulsion explosives are basically composed of a continuous phase of a carbonaceous fuel, a dispersive phase of an aqueous solution of an inorganic oxidate, an emulsifier, and a foam retainer.
A W/O type emulsion explosive having an initiating sensitivity of improved aging stability at small calibers and low temperatures by using a specific emulsifier such as a mixed emulsifier consisting of a specific mixing proportions of sorbide fatty acid ester, sorbitan fatty acid ester and sorbitol fatty acid ester, is known from Japanese Patent Application Laid-open No. 59-207,889. The carbonaceous fuel practically used therein is a petroleum wax such as microcrystalline wax or a hydrocarbon oil obtained by purifying a lubricant fraction such as fluid paraffin.
A W/O type emulsion explosive of an improved aging stability by using in combination a specific emulsifier such as an emulsifier having a hydrophobic group consisting of a long chain unsaturated fatty acid, for example, sorbitan monooleate, and a petroleum wax such as microcrystalline wax containing 30% or more of urea non-added component or paraffin wax, etc., is known from Japanese Patent Application Publication No. 60-8,988.
A W/O type emulsion explosive having a sympathetic detonation sensitivity of improved aging stability by using a carbonaceous fuel not containing an oil fraction and containing a polymer selected from epoxy resin, unsaturated polyester resin, polybutene, isobutyrene, petroleum resin, butadiene resin, is proposed by Japanese Patent Application Laid-open No. 61-40,892. The petroleum resin used therein is a C.sub.5 series or C.sub.9 series petroleum resin derived by polymerizing the fractions obtained in the naphtha-cracking process, and preferably has a molecular weight of 1,000-1,400.
A W/O type emulsion explosive of the same purpose using a polymer selected from a polymer or a copolymer of .alpha.-olefin, a polymer or a copolymer of pentadiene, and an alicyclic hydrocarbon resin, as the carbonaceous fuel, is also proposed by Japanese Patent Application Laid-open No. 61-40,893. The polymer of .alpha.-olefin used therein is a polymer prepared mainly from .alpha.-olefin having 6-14 carbon atoms and a general formula of CH.sub.2 .dbd.CH--R wherein R represents an alkyl group, which polymer preferably has a molecular weight of 300-100,000, more preferably has a molecular weight of 300-3,000 and a liquid state at ambient temperature. In its preparation examples, a polymer of .alpha.-olefin, which has a molecular weight of about 7,000 (Trade name "Riboloop 70", pour point -55.degree. C., produced by Lion Yushi K.K.), is only shown as suitable. The polymer is an oligomer of .alpha.-olefin, which is liquid at ambient temperature.
A W/O type emulsion explosive of improved aging stability using simultaneously an oil content such as gear oil, a polymer selected from a polyethylene wax of a number average molecular weight of 500-5,000, a polypropylene of an average molecular weight of not exceeding 5,000, and an atactic polypropylene of an average molecular weight of not exceeding 15,000, as the carbonaceous fuel, is also proposed by Japanese Patent Application Laid-open No. 57-149,893. In its examples, polyethylene wax is shown to have number average molecular weights of 300, 500, 2,000, 5,000, and 8,000, and no mention is made about melting point, density and terminal group, nor about trade names of the used polyethylene waxes.
Meanwhile, a W/O type emulsion explosive, for a purpose of hardening the emulsion, using a specific emulsifier, i.e., specific amounts of fatty acid and fatty acid soap, as well as a mixture of a specific proportion of sorbide fatty acid ester, sorbitan fatty acid ester and sorbitol fatty acid ester, is known from Japanese Patent Application Laid-open No. 62-162,685. In its examples, practically used carbonaceous fuel is a fluid paraffin or a petroleum wax, such as microcrystalline wax or paraffin wax, etc.
The above prior W/O type emulsion explosive wherein a specific emulsifier or a combination of a specific emulsifier and a specific petroleum wax is used has a drawback in that the explosive does not harden sufficiently, though the aging stability thereof is improved.
The above prior W/O type emulsion explosive wherein a specific polymer is used as a carbonaceous fuel has drawbacks in that it has frequently a high viscosity and a high adhesive power to result in difficulty in the production process, and that it does not harden sufficiently, though the shelf stability thereof is improved.
The above prior W/O type emulsion explosive wherein an oligomer of .alpha.-olefin which is liquid state at ambient temperature is used as a carbonaceous fuel has drawbacks in that it has a high adhesive power and does not harden sufficiently, though aging stability of the sympathetic detonation sensitivity is improved.
The prior W/O type emulsion explosive wherein polyethylene wax is co-used with the oil content has drawbacks in that the characteristic property thereof is not improved, if the polyethylene wax has a number average molecular weight of less than 350, and that the aging stability of the initiating sensitivity is deteriorated. In addition, even when a polyethylene wax of a number average molecular weight of 350-1,000 is co-used as the carbonaceous fuel in the production process of the W/O type emulsion explosive, the production has a difficulty depending on the terminal group in that the emulsification is hardly performed when the terminal group of the wax is a carboxylic group.
The prior W/O type emulsion explosive wherein a specific amount of a fatty acid or fatty acid soap is used and a mixture of a specific proportion of emulsifiers is used has drawbacks n that an emulsion explosive of constantly stable properties is hardly obtained, and that the characteristic properties thereof are restricted and still insufficient.
A prior W/O type emulsion explosive wherein an oil of a high melting point or high softening point as the carbonaceous fuel is reciped and co-used with an emulsifier can produce an emulsifier which is hard to some extent by reciping large amounts of the oil and the emulsifier and adjusting the reciping proportion thereof. However, it has a drawback i that the aging stability of the initiating sensitivity of the emulsion explosive is deteriorated due to the increase of the amounts of the emulsifier and the oil of a high viscosity.
If the W/O type emulsion explosive is soft in its characteristic property, the product emulsion explosives, particularly those of small calibers, are liable to deform during the transportation, and difficult in handling in that they are difficult to charge in small bores due to their deformation in charging. Such deformation is a cause of insufficient effect of detonation or a cause of non-detonation.
A W/O type emulsion explosive is requested to have a good aging stability, because it is often used after about 6-12 months at the longest from the production thereof.
However, a W/O type emulsion explosive having sufficiently satisfiable aging stability and shape-holding hard property has not yet been proposed, so that such emulsion explosive has been earnestly desired.